nest-object-deep-copy

Deep Copy Nested Objects

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What

This is pure javascript function that aims to create a real hard copy from original javascript object.

Why

• It is just a pure function and final import size is only 662 bytes.
• It gives you the real hard copy, avoids limitations of using spread operator, Object.assign and JSON.parse(JSON.stringify(object)).

Feature	JSON.parse(JSON.stringify(object))	spread operator / Object.assign	nest-object-deep-copy
Hard Copy nested object	✔️	❌	✔️
Copy functions	❌	✔️	✔️
Keep prototype chain	❌	❌	✔️
Circular Reference	Throw Error	Keep Circular Ref	Graceful Handle

Gracefully handle Circular Reference

const originalObject = { 
  a: 'test',
  f: 1
};
originalObject.a = originalObject;
originalObject.b = {};
originalObject.b.c = originalObject;

deepCopy(originalObject) will result in:

{ 
  a: '[Circular]',
  f: 1,
  b: {
    c: '[Circular]',
  },
};

Limitions of common ways

Cannot make hard copy on nested objects

let user = {
  id: 101,
  gender: 'male',
  personalInfo: {
    name: 'Jack',
  }
};

Then the spread operator or Object.assign() WILL NOT give you a hard copied object:

let copiedUser = {
  ...user
};

// Change a nested object value
copiedUser.personalInfo.name = 'Tom';

// Change a property which holds a primitive value
copiedUser.id = 2;

// original user object mutation happens
console.log(user.personalInfo.name); // 'Tom'
console.log(copiedUser.personalInfo.name); // 'Tom'

// BUT mutation does not happen to property which holds a primitive value
console.log(user.id); // 1
console.log(copiedUser.id); // 2

Loosing functions

let user = {
  id: 1,
  name: 'jack',
  speak: function() {
    console.log('I am speaking from original object.');
  }
};

let copiedUser = JSON.parse(JSON.stringify(user));

user.speak(); // `I am speaking from original object.`
copiedUser.speak(); //Uncaught TypeError: copiedUser.speak is not a function

Loosing prototype chain

// Declare a constructor function
function Foo(who) {
  this.me = who;
}

// Now there is a new property called 'identify' which equals to a function in prototype chain of any object being created by calling new Foo
Foo.prototype.identify = function() {
  return 'I am ' + this.me;
}

// Create a user object by constructor Foo
const user = new Foo('Jack');

// Create a copy object by using spread operator
const copiedUser1 = {...user};
// Prototype chain is lost !!
copiedUser1.identify(); // Uncaught TypeError: copiedUser1.identify is not a function

// Create a copy object by using Object.assign()
const copiedUser2 = Object.assign({}, user);
// Prototype chain is lost !!
copiedUser2.identify(); // Uncaught TypeError: copiedUser2.identify is not a function

// Create a copy object by using JSON.parse(JSON.stringify(object))
const copiedUser3 = JSON.parse(JSON.stringify(user));
// Prototype chain is lost !!
copiedUser3.identify(); // Uncaught TypeError: copiedUser3.identify is not a function

Install

$ npm install nest-object-deep-copy

How to use it

const deepCopy = require('./nest-object-hard-copy');

//Get a hard copy
let copiedUser = deepCopy(object);

License

This project is licensed under the MIT License